Planetary transmissions are frequently used as speed changers, either to reduce or increase the speed of one shaft with respect to another. Normally, these mechanisms provide coaxial shaft sections and a third reference controlling the fixed or rotative movement of the axis of the planetary members about the central shaft axis. Any one of these three references can be held fixed, or subject to braking action, with correspondingly modified output-input relationships of the other two references. Normally, planetary transmissions involve intermeshed gears, presenting noise and wear problems at unusually high speeds. In particularly small devices, these problems become acute. Planetary power transmissions operating on mere friction have been resorted to in an attempt to avoid this problem, but it has been extremely difficult to generate adequate but not excessive pressure at the interengaged rolling surfaces to assure freedom from slippage without undue wear. The present invention provides a solution to this problem.